Apparatus for synchronizing oscillation of read/write heads with the rotation of a data storage disc pack

ABSTRACT

Apparatus is described for oscillating the read/write head carriage of a rotary drive mechanism for data storage disc pack. An optical sensing device is employed to determine the angular phase and frequency of rotation of the disc pack, and a phase discriminator compares the sensed frequency with the output of an oscillator to phase-lock the oscillator thereto. The resulting oscillation signal is fed to an electromagnetic actuator to cause oscillation of the read/write head in synchronism with the rotation of the disc pack.

United States Patent 1 1 Sordello [451 Apr. 17, 1973 [54] APPARATUS FORSYNCHRONIZING OSCILLATION OF READ/WRITE HEADS WITH THE ROTATION OF ADATA STORAGE DISC PACK [75] Inventor: Frank JfSordellm san Jose, Calif m95123 [73 Assignee: Information "'smiag' System; Inc.,

Cupertino, Calif.

[22] Filed: Aug. 16, 1971 21 Appl. No.3 172,141

[52] US. Cl. ..340/I74.l C, 346/137 [51] Int. Cl. ..GIlb 5/00 [58] Fieldof Search ..340/174.l B, 174.1 C; 346/74 MD, 137; 274/41.4

[56] References Cited UNITED STATES PATENTS 3,126,535 3/1964 Streeter..340/174.1 C 3,427,606 2/1969 Black et al. ..340/174.1 8 2,862,38912/1958 Potter ..340/174.1 C 3,177,476 4/1965 Robinson ..340/174.1 C3,208,057 9/1965 Applequnt, Sr. et al ..340/174.1 C

POSITION SERVO SYSTEM OTHER PUBLICATIONS Time Base Compression for VideoRecording" by Lawrence et al., IBM Tech. Disc. Bul. Vol. 13, No. 4 Sept.1970 t Primary ExaminerVincent P. Canney Attorney-C. Michael Zimmermanand Gerald L. Moore [5 7] ABSTRACT Apparatus is described foroscillating the read/write head carriage of a rotary drive mechanism fordata storage disc pack. An optical sensing device is employed todetermine the angular phase and frequency of rotation of the disc pack,and a phase discriminatorcompares the sensed frequency with the outputof an oscillator to phase-lock the oscillator thereto. The resultingoscillation signal is fed to an electromagnetic actuator to causeoscillation of the read/write head in synchronism with the rotation ofthe disc pack.

6 Claims, 1 Drawing Figure P1 1115? DISCRIMINATOR VdiITTeT CONTROLLEDOSClLLATOR PATENTEDAPR 1 11915 728 699 vosmou w SERVO v SYSTEM PHASEMSCRIMINATOR VOLTAGE CONTROLLED' Y OSClLLATOR I J Z Q INVENTOR.

1 firank .or clello ATTORNEY.

APPARATUS FOR SYNCHRONIZING OSCILLATION OF READ/WRITE HEADS WITH THEROTATION OF A DATA STORAGE DISC PACK BACKGROUND OF THE INVENTION Thisinvention relates to direct access data storage devices and, moreparticularly, to apparatus for oscillating a data transfer device, e.g.,a read/write head, in a predetermined manner related to the rotation ofa data storage device such as a pack of magnetic discs.

As the speed of the central processing units of computers has increased,there has been a strong demand that the speed with which data orinformation is transferrable between data storage devices and a computerbe correspondingly increased. For this reason, direct access datastorage devices of the type employing a pack of rotating magnetic discsfor memory are being widely adopted. Such devices have the advantage ofenabling information to be either transferred to, or removed from,randomly selected locations or addresses without the necessity of thedevice having to serially seek the desired location such as must be donewith, for example, magnetic tape memories.

It will be appreciated that for a random access disc pack storage deviceto be effective, one must be able to quickly and precisely position theread/write heads at specified address locations with respect to therecording discs. For this reason, sophisticated positioning apparatusesand position sensing systems, such as that described in the nowabandoned U.S. Pat. application, Ser. No. 63,508 entitled PositionSensor T. W. Martin et al., filed Aug. 13, 1970, have been developed.Precise positioning systems of this nature need to be continuallycalibrated in view of their reliable on light sources and sensors whichhave somewhat variable outputs. It has been the practice in order toobtain this calibration to slightly wiggle or oscillate the read/writehead carriage. This slight oscillation imposes controlled variations onthe outputs of the various photo sensing devices and enables acomparison of the same to correct for undesired discrepancies.

Oscillation of the read/write head carriage also causes the headsthemselves to oscillate with respect to the recording discs. Becausetheir oscillation has been slight, e.g., i128 micro-inches, it has, inthe past, been acceptable. That is, the oscillation of each head withrespect to the optimum positioning of the head on a disc recording trackhas not prevented the head from either picking up data previouslyrecorded on the track or from writing data onto the track. However, theoscillation has required that adjacent tracks be spaced apart a distancesufficient to prevent overlapping of tracks or, in other words,crosstalk."

As man's usage of computers and other data utilization devices hasincreased, the demand for greater data storage capabilities has alsogrown. For this reason, those in the art have been desirous of spacingadjacent tracks on recording discs as close together as they can. Mucheffort has been devoted to this end. Most of such effort, however, hasbeen directed to eliminating the necessity of the wiggle," either byattempting to develop other positioning sensing systems not requiringcalibration for accuracy, or by developing other calibration schemes.Such efforts, though, have not yielded the performance that the wigglemethod has.

SUMMARY OF THE INVENTION The present invention eliminates the problem oftrack overlapping while still enabling a wiggle for calibration purposesto be superimposed on the read/write head carriage. It accomplishes thisby synchronizing the head carriage oscillation with the angularfrequency of rotation of the discs in such a manner that each read/writehead always describes the same path with respect to its associated discat each track radial position, and so that all radial track positions ofthe head on the disc are concentric and uniformly shaped. To these ends,the apparatus of the invention broadly includes means for sensing theangular phase and frequency of a rotating storage device, e.g., a packof rotating magnetic discs. It further includes means responsive to thesensed angular phase and frequency by causing the frequency of theoscillation signal which drives the head carriage in the desiredoscillatory motion to be related to such angular phase and frequency ina predetermined manner. This results in the oscillatory motion of theread/write heads to also be related in a predetermined manner to theangular phase and frequency of the rotating disc pack. Because of such,the adjacent tracks of each read/write head on its corresponding disccan be made to uniformly follow one another, at set distances apart,rather than oscillate with respect to one another.

Most desirably, the predetermined relationship between the rotation ofthe disc pack and oscillation of the head carriage is obtained bysynchronizing the phase of the oscillation signal driving the headcarriage with the angular phase and frequency of rotation of the discpack. This will assure that the desired relationship between adjacenttracks, and time-spaced seeks on the same track, is most simplyobtained.

BRIEF DESCRIPTION OF THE DRAWING With reference to the accompanyingsheet of drawing:

The single FIGURE is a schematic and block diagram of a preferredembodiment of the synchronizing apparatus of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the drawing, aplurality of discs 11, each one of which has its surfaces coated with amagnetic material, are illustrated coaxially secured together to form adisc pack 12. In use, the disc pack 12 is axially rotated, and data indigital form is selectively transferred onto or from tracks on the discsurfaces by corresponding data transfer devices in the form ofread/write heads 13. As is illustrated, a head 13 is provided for eachactive disc surface, and each head is mounted on the free end of asupport arm 14 therefor cantilevered from a carriage 16.

The carriage 16 is secured to the moving coil 17 of an electromagneticactuator 18. The actuator 18 is energized by a position servo system,represented diagrammatically by block 19, to translate carriage 16, and,hence, the read/write heads 13 radially of the disc pack 12 and holdthesame at various radial locations with respect to the disc surfaces. Eachradial location of a head on a surface corresponds to a closed loop pathor track of the head over the surface formed by rotation of the pack.Data is transferrable between each head and its associated disc surfaceon each one of such tracks. 7

It will be apparent that for proper and efficient operation, it isnecessary that each of the heads be precisely positionable at itsvarious track locations. Positioning and positioning sensing means forcontrolling the actuator 18, such as that disclosed in the previouslymentioned application, Ser. No. 63,508, have been developed for thispurpose. Such systems, though, require that the head carriage beoscillated slightly at each position thereof in order to assure that thesensing arrangement is properly calibrated. An oscillator is thereforeincluded to superimpose the desired oscillation on the position servosystem.

Oscillation of the head carriage will cause a corresponding oscillationof each head with respect to its associated disc surface. As has beenbrought out previously, this slight oscillation has required thatadjacent recording tracks be spaced some distance apart in order toprevent the oscillation or wiggle from causing the head, when it ispositioned at a particular track, from crossing over onto adjacenttracks and either reading the wrong data from the disc or writing dataonto the wrong track. This has placed a limit on the number of trackpositions available on a disc surface and, hence, a limit on the amountof data which can be stored on a surface.

In accordance with the present invention, apparatus is included foreliminating the necessity of adjacent tracks being spaced from oneanother an additional distance to permit the head carriage to beoscillated for calibration of the positioning sensing system. In thisconnection, means are provided for sensing the angular phase andfrequency of rotation of the disc pack 12. That is, one of the discs,disc 11, is provided at a predetermined location with a discontinuitywhich can be sensed during rotation of the pack. In this preferredembodiment, the discontinuity is in the form of a slot or notch 21extending radially inward of disc 11 a short distance from its outerperipheral edge. An optical sensor or transducer is positioned at apredetermined location with respect to disc 11' for indicating thepassage thereby of the slot 21 during rotation of the disc pack. Suchsensor includes a U-bracket 22 having a light emitting device, such as asolid state light source 23, on one leg thereof facing a light sensor,such as a photo transistor, on the other leg thereof. As is illustrated,the sensing device is positioned straddling the peripheral edge of disc11' so that the disc edge blocks transmission of light between source 23and sensor 24 except when the notch 21 passes therebetween. This willresult in the photo sensor being energized to form an electrical pulseonce every revolution of the disc 11' and, hence, once every revolutionof disc pack 12. The phase and frequency of occurrence of such pulses,hereinafter called index pulses," will thus indicate the angular phaseand frequency of rotation of the disc pack 12. Specifically, such phaseand frequency of occurrence will be equal to the angular phase andfrequency of rotation of the disc pack.

The index pulses generated by the photo sensor 24 on rotation of thedisc pack are fed into an amplifier 26 where the same are not onlyamplified, but also shaped to provide a more precise indication of theirphase and frequency. The pulse signal emanating from the amplifier isschematically illustrated at 27.

The invention further includes means responsive to the sensed angularphase and frequency of the rotating storage device by causing thefrequency of the output signal from oscillator 20 to be related in apredetermined manner to the frequency of rotation of the disc pack. Thatis, the output pulse signal from amplifier 26 is fed into a phasediscriminator 28 which drives the oscillator 20. Such oscillator is avoltage controlled oscillator, and its output is also fed into the phasediscriminator via feedback loop 29. The phase discriminator compares thephase of the output signal of the oscillator with the index pulses fromamplifier 26 and phase locks the oscillator output to the phase andfrequency of occurrence of the index pulses. This will result in thephase and frequency of the oscillation signal produced by the oscillator20 being equal to the phase and frequency of occurrence of the indexpulses and, hence, equal to the angular phase and frequency of rotationof the disc pack 12. This synchronism of the phase and frequency of theoscillation signal with the angular phase and frequency of the disc packprovides the desired relationship of the oscillatory motion of the leadcarriage with the rotation of the disc pack.

As is indicated by the reference numeral 31, the output oscillationsignal from oscillator 20 is in the form of a sawtooth wave. In order toprevent the sharp changes in direction of such signal from causingabrupt changes in the direction of mechanical oscillation of the heads13, the sawtooth signal is passed through a filter 32 which converts thesame into a generally sinusoidal waveform 33 for superimposition on theposition servo system 19. it should be noted that although a sinewave isused in this embodiment, other types of oscillation waveforms, such asthe sawtooth waveform directly or even a square waveform, may be used.

The dotted line circles 34 and 36 on the upper surface of the top disc11 represent two adjacent tracks which are produced when the oscillationof the heads 13 is synchronized with the phase and frequency of rotationof the disc pack in accordance with this preferred embodiment of theinvention. As is illustrated, the tracks are concentric circles whichare eccentric with respect to the axis of rotation of the disc pack. Thecircular track form is caused because the frequency of the oscillationis equal to the angular frequency of rotation of the disc pack. Theeccentricity of such circles is caused by the oscillation. That is, the

movement of each head through one cycle of oscillatory motion as thedisc pack rotates one revolution results in the track of the headdescribing a circle on the surface whose center is spaced a distanceequal to one-half the amplitude of the oscillation from the axis ofrotation of the discs.

In accordance with the preceding description of the invention, eachrecording head is moved radially with respect to the disc as the discrotates. The radial movement of the head is the same both in magnitudeand direction at the same radial position of each recording trackthereby allowing for an increase in track density over prior recordingdevices. The increased track density is possible because the oscillatorymotion of each head is in phase with the phase of the rotation of thedisc pack. As a result the adjacent circular tracks will all beeccentric in the same direction, i.e., have the same center. Thus,problems of track overlapping and consequent crosstalk are obviated, andadjacent tracks can be positioned quite close together. In fact,utilization of the invention in one particular disc drive mechanism hassubstantially contributed to the elimination of total off-tracktolerances such that the number of tracks per radial inch which can bewritten on a disc surface was doubled without crosstalk.

It 'will be recognized by those skilled in the art that various changescan be made within the scope of the invention. For example, although forsimplicity it is preferred that the oscillation of the heads be equal inboth frequency and phased to the angular phase and frequency of rotationof the disc pack, this is not necessary from the broad standpoint. Suchoscillation frequency could be multiples of the angular frequency ofrotation of the disc pack, as long as an appropriate phase relationshipwas maintained to assure that the heads will follow the same trackwhenever positioned at any particular track location. Moreover, althoughit is preferred to continually monitor the angular phase and frequencyof the disc pack so that any changes in its frequency can be reflectedin the oscillatory motion of the heads, one could also merely spot-checkthe angular phase and frequency of the disc pack and set the oscillatorymotion of the heads accordingly.

I claim:

1. Apparatus for oscillating a data transfer device with respect to arotating data storage device comprising means for sensing the angularphase and frequency of said rotating storage device, means forgenerating an oscillation signal, means responsive to the sensed angularphase and frequency of said rotating storage device by causing the phaseand frequency of the oscillation signal to be related in a predeterminedmanner to the phase and frequency of rotation of said storage deviceduring each rotation of the storage device, and means for converting theresulting oscillation signal into corresponding oscillatory motion ofsaid data transfer device with respect to said storage device wherebythe oscillatory motion of said data transfer device is also related in apredetermined manner to the angular frequency of said rotating storagedevice.

2. The apparatus of claim 1 for oscillating a data storage devicewherein said means for sensing the angular phase and frequency of saidrotating storage device continually senses the same during oscillationof said data transfer device, and said means responsive to the sensedangular phase and frequency of said rotating storage device maintainsthe phase and frequency of the oscillation signal in said predeterminedrelationship to the phase and frequency of rotation of said storagedevice during oscillation of said data transfer device.

3. The apparatus of claim 1 for oscillating a data transfer devicewherein said means for converting the resulting oscillation signal intocorresponding oscillatory motion of said data transfer device producedoscillatory motion of said data transfer device having substantially thesame frequency as the frequency of said rotating storage device.

4. The apparatus of claim 1 for oscillating a data transfer devicewherein said data storage device comprises a pack of coaxial magneticdisks which are axially rotated, and said means for sensing the angularphase and frequency of said rotation thereof mc udes an opticaltransducer responsive to the passage thereby of a discontinuity in oneof said discs by generating a signal indicative of the angular phase andfrequency of rotation of said pack.

5. The apparatus of claim 4 for oscillating a data transfer devicewherein said means responsive to the sensed angular phase and frequencyof said rotating data transfer device includes a phase discriminator forphase locking the output of said means for generating an oscillationsignal to the frequency of the signal generated by said opticaltransducer to thereby phase lock said output with the phase andfrequency of rotation of said disc pack to provide said predeterminedrelationships between the frequency and phase of the disc pack rotationand oscillatory motion of the data transfer device.

6. The apparatus of claim 5 for oscillating a data transfer devicewherein means are provided for filtering the output signal of said meansfor generating an oscillation signal to produce a sinusoidal waveformtherefrom for direction to said means for converting said oscillationsignal into oscillatory motion of said data transfer device.

1. Apparatus for oscillating a data transfer device with respect to arotating data storage device comprising means for sensing the angularphase and frequency of said rotating storage device, means forgenerating an oscillation signal, means responsive to the sensed angularphase and frequency of said rotating storage device by causing the phaseand frequency of the oscillation signal to be related in a predeterminedmanner to the phase and frequency of rotation of said storage deviceduring each rotation of the storage device, and means for converting theresulting oscillation signal into corresponding oscillatory motion ofsaid data transfer device with respect to said storage device wherebythe oscillatory motion of said data transfer device is also related in apredetermined manner to the angular frequency of said rotating storagedevice.
 2. The apparatus of claim 1 for oscillating a data storagedevice wherein said means for sensing the angular phase and frequency ofsaid rotating storage device continually senses the same duringoscillation of said data transfer device, and said means responsive tothe sensed angular phase and frequency of said rotating storage devicemaintains the phase and frequency of the oscillation signal in saidpredetermined relationship to the phase and frequency of rotation ofsaid storage device during oscillation of said data transfer device. 3.The apparatus of claim 1 for oscillating a data transfer device whereinsaid means for converting the resulting oscillation signal intocorresponding oscillatory motion of said data transfer device producedoscillatory motion of said data transfer device having substantially thesame frequency as the frequency of said rotating storage device.
 4. Theapparatus of claim 1 for oscillating a data transfer device wherein saiddata storage device comprises a pack of coaxial magnetic disks which areaxially rotated, and said means for sensing the angular phase andfrequency of said rotation thereof includes an optical transducerresponsive to the passage thereby of a discontinuity in one of saiddiscs by generating a signal indicative of the angular phase andfrequency of rotation of said pack.
 5. The apparatus of claim 4 foroscillating a data transfer device wherein said means responsive to thesensed angular phase and frequency of said rotating data transfer deviceincludes a phase discriminator for phase locking the output of saidmeans for generating an oscillation signal to the frequency of thesignal generated by said optical transducer to thereby phase lock saidoutput with the phase and frequency of rotation of said disc pack toprovide said predetermined relationships between the frequency and phaseof the disc pack rotation and oscillatory motion of the data transferdevice.
 6. The apparatus of claim 5 for oscillating a data transferdevice wherein means are provided for filtering the output signal ofsaid means for generating an oscillation signal to produce a sinusoidalwaveform therefrom for direction to said means for converting saidoscillation signal into oscillatory motion of said data transfer device.